Signal transmission system



g- 22, 1939- B. G. BJORNSON ET AL SIGNAL -TRANSMISSION SYSTEM Filed Aug. 10, 1938 3 Sheets-Sheet 1 ,5. a. BJORNSON INVENTORS An N ug- 22, 1939- B. G. BJORNSON ET AL 9,397

SIG'NAL TRANSMISSION SYSTEM Filed Aug. 10, 1938 :s Sheewjs-Sheet 2 INVENTORSI a. a. 'BJORNSON N. W BRYANT ATTORNEY Aug. 22, 1939. B. G BJORNSON ET AL SIGNAL TRANSMISSION SYSTEM Filed Aug. 10, 1938 3 Sheets-Sheet fww wow q 3 rl T /NVENTORS:' B. G. BJORNSON M W BRMNT W flinZA ATTORNEY Patented Aug. 22, 1939 UNITED STATES SIGNAL TRANSMISSION SYSTEM Bjorn G. Bjornson, New York, N. Y., and Newton W. Bryant, Lyndhurst, N. 3., assignors to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application August 10, 1938, Serial No. 224,087

16 Claims.

This invention relates to signal transmission systems and particularly to circuits for controlling the volume on signal transmission systems.

One object of the invention is to provide a signal transmission line with volume control circuits that shall be governed according to the operation of a volume indicator to maintain substantially constant volume on a transmission line.

Another object of the invention is to provide a signal transmission line with volume control circuits of the above-indicated character that shall efiect gains and losses of diiTerent amounts according to the energy of the signals on the transmission line.

Another object of the invention is to provide a signal transmission line with a volume integrat ing detector circuit for counting the amplitude variations above a predetermined value and a cumulative timer for determining the time interval during which amplitude variations are counted by the volume detector circuit that shall effect a small increase in gain under control of the timer circuit in case a minimum number of amplitude variations are not counted by the volume detector circuit during a time interval and that shall effect no change in gain or difierent amounts of gain loss in case the minimum number or more than the minimum number of amplitude variations are counted during a time interval by said volume detector circuit.

A further object of the invention is to provide a signal transmission line with a syllable counter operated by signal syllables and a second volume integrating detector circuit that shall effect a substantial increase in gain under control of the syllable counter when the detector circuit is not operated by amplitude variations above normal value and a predetermined number of syllables are counted and that shall effect no gain or gain of varying amounts when the syllable counter is operated by a predetermined number of syllables and the volume detector circuit is operated by one or more amplitude variations above normal value.

In signal transmission systems it is desirable and in some cases essential to control the volume of the transmitted signals. In transmitting speech currents to radio transmitting stations it is desirable to hold the volume of the transmitted speech current at constant volume in order not 'to overload apparatus at the radio transmitting station. A system of this type is disclosed in the patent to S. Doba, Jr. 2,012,810, August 27, 1935.

.In th p en invenj qn v u e ontra-.1 Cir cuits that operate according to the principal of operation of a volume indicator are employed to maintain substantially constant volume. on a transmission line. A volume indicator is an instrument employed to read the volume of signals on a transmi'ssionline and essentially consists of a damped voltmeter. Volume readings are obtained by reading the number of swings of the instrument needle for a given time interval. The time interval is generally taken at ten seconds.

. A four-wire system has been employed to describe the invention. The gain on the transmitting channel is controlled by an' amplifier governed by a motor operated potentiometer. Essentially the circuits employed to control the motor operated potentiometer comprise a cumulative timer circuit, a first volume integrating detector circuit, a fast gain decreaser circuit and a large gain increaser circuit which. employs a syllable counter and a second volume integrating detector circuit. The cumulative timer circuit measures the time interval during which the .first volume integrating detector circuit counts amplitude variations above a predetermined value. b The cumulative timer circuit is provided with a timer relay which operates according to the peaks of the speech currents on the transmission line. The timer relay. charges a condenser according to the operation thereof. The charge I on the condenser measures the time interval during which the amplitude variations are counted.

The cumulative timer circuit regulates the length of the time interval by integrating the time during which useful outgoing speech is present on the transmission line. When this time interval has become five seconds the interval is terminated. Since in connected conversation useful speech is present 65 to 75 per cent of the time the total elapsed time is usually about seven seconds. This time interval was arbitrarily choosen instead of the ten-second interval usually associated with volume indicator readings. It is to be understood that any other desired time interval may be chosen if so desired. A gain inv creaser relay is operated under control of the charge on the timer condenser at the end of the time interval.

The first volume integrating detector circuit is provided with two marginal relays. The first marginal relay is operated by syllables having a predetermined amplitude and the second marginal 'relay is 2 decibels less sensitive than the first marginal relay. The second marginal relay will only be operated when the output volume in- V ldicatorzoyershoots at least 2 decibels.

If the first volume integrating detector circuit does not count a minimum number of syllables on the transmission line by means of the first marginal relay during a time interval measured by the cumulative timer circuit, the cumulative timer circuit governs the motor operated potentiometer to eiTect a small gain on the transmission line. The gain effected on the transmission line may be of the order of three-fourths decibel and two counted syllables may be taken as the minimum number counted by the first marginal relay. have been two, three or four operations of the first marginal relay in the time interval, then, no gain change is made on thetransmission line and a new time interval is started; If five op-' erations of the first marginal relay take place in a time interval the gain on a-transmission line is immediately decreased three-fourths decibel and a new time interval is started. Small gain changesor adjustments arecontinued upor downunless higher gain changesare required.

If during any given time interval as. determined by the cumulative timer circuit there .are three strong syllables which cause operation of the second marginal relay, then circuit modifications are .made so that any gain decrease occurring during that time interval will .be ,3 decibels instead of the usual three-fourths decibel. The 3 decibel gain decrease occurs immediately after the fourth operationof the second marginal relay or the fifthoperation ofthe first marginal'relay. If within the time interval there are .not four syllables strong enough to operate the second marginal relays or five syllables strong, enough to operate the first marginal relay, the circuits are all returned to normal position without any gain change.

The fast gain decreaser circuit produces a gain decrease on any syllable with a peak that eX- tends above the marginal operating level of the fast ,decreaser circuit. This circuit is nearly peak operated because very fast operation is desired. Since peak factors of various talkers vary over a wide range, this type-of circuit by itself cannot be expected to give goodregulation based on the readings of ,a volume indicator. 'The sensitivity of the circuit is adjusted so that it very seldom reduces the volume too low but generally leaves it a little high so that the circuits described above will make the more accurate volume adjustments.

The fast gain increaser circuit is made up of a syllable counter and a second volume integrating detecting circuit. Six successive low syllables must be counted before any gain. increase can be effected by means of the large gain increaser circuit. After the sixth low syllable the gain on the transmission line is increased 15 decibels, 8 decibels, 3 decibels, or no decibels, according to the operation of the second volume .integrating detector circuit. Three marginal relays are controlled by the second volume integrating detector circuit. If none ,of the marginal vrelays under consideration are operated during the operation of the syllable counter, then a gain increase of 15 decibels is effected undercontrol of the syllable counter. If one or more syllables is strong enoughto operate themost sensitivemarginal relay, but notstrong enough to operate the others, then the gain increase is reduced to 8 decibels. If one or more syllables is strong enough to operate the second marginal relay, which is more sensitive than the first, but not stron If at the end of a time .interval there .nearly peak operated whereas the volume integrating detector circuit should require considerable power for operation. The cumulative .-timcrcircuit is set so sensitive that it will be operated a large part of the time during which speech is present, The sensitivity of the cumulative timer circuit is limited by the noise level.

Th e fast gain decreaser circuit will operate only on exceptionally high peaks which seldom occur when gain adjustment is fairly correct.

In the,accompanyingdrawings,Figs. l, 2 and 3 disclose diagrammatic circuitsconstructed in ac cordance with the invention. The drawings are assembled to show the completed circuits by attaching Fig.2 to the right side of Fig. 1 and by attaching Fig. 3 to the bottom of Fig. 1.

Referring to Figs. .1, 2 and 3- of the drawings. a transmission system is shown comprising a transmitting channel I and a receiving channel 2. The receiving-channel comprises conductors 3 and 4. An amplifier space discharge device 5 comprising a grid 6, an anode 1 and a cathode 8 is effectivelyconnected in series-with the transmitting channel. A motor operated potentiometer 9 controls thedevice 5 to govern the gain on the transmission channel I so as to maintain the volume substantially constant. The portion of the transmitting-channel l shown on thedrawings comprises input conductors 9a and .ltwhich are connected by a transformer ,l l to the potentiometer 9 adjacent to the device 5. The output circuit from the device 5 is connected by a transformer 12 to a suitable amplifier iii. The amplifier I3 isconnected to a second amplifier l4. The

output circuit from the amplifier i4 is connected by a transformer l5 to output conductors l6 and IT. A condenser H3 is connected across the secondary winding of the transformer l and a resistance I9 is connected across the-primary winding of the transformer 12. .Anode potential for the anode l is provided by a batteryzfl in circuit with an inductance element 2!. Two by-pass condensers 22 are associated with thedevice 5. A condenser 23 shunted by a resistance element 24 is connected to the cathode 8 for providing .the biasing. potential for the device 5. The plate current of device 5 flows through resistance 24 and the resulting voltage across it is inthe grid circuit and biases the device properly. A re sistance 300 and one of the condensers .22 provide some filtering action.

The potentiometer ii is motor-operated and comprises a resistance element 25 controlled by a switch arm 26 mounted on a shaft 21. The shaft 2'! is operated in a forward and in a reverse direction by a constantly operating motor 28 under control of two magnets 29 and 30. The magnet 29 is fixedly connected to slip rings 3| and a pinion 32. The pinion 32, the slip rings 3| and the magnet 29 are rotatably supported on the shaft 2'1. An armature 33 is slidably mounted on the shaft 21 to be rotated therewith and adapted to be engaged by the magnet 29 when energized. The magnet 30, slip rings 34 and a gear wheel 35, are rotatably mounted on the shaft 21. The magnet 36 when energized is adapted to engage an armature 36 which is slidably mounted on and adapted to rotate with the shaft 21. A motor shaft 31 carries a beveled gear wheel 38 which meshes with two beveled gear wheels 39 and 46. The beveled gear wheel 39 has a pinion 4| fixed thereto which meshes with the gear wheel 35. The beveled gear wheel 40 has a gear wheel 42 fixed thereto which meshes with the pinion 32.

In the motor-operated potentiometer above described, the magnet 36 is constantly rotated at a slow rate of speed and the magnet 29 is constantly rotated at a faster rate of speed. Upon energization of the magnet 39 the contact arm 26 which is attached to the shaft 21 is moved toward the right as shown in Fig. 1 of thedrawings to raise the gain on the transmitting channel. When the magnet 29 is energized, the con tact arm 26 is moved toward the left as shown in Fig. 1 of the drawings to lower the gain on the transmitting channel I. The raising of the gain is effected at a much lower speed than the lowering of the gain.

The magnets 29 and 36 of the motor-operated potentiometer are controlled by means of 'a cumulative timer circuit 43, a volume integrating detector circuit 44, a peak-operated large gain decreaser circuit 45, a syllable counter circuit 46 and a second volume integrating detector circuit 41. The cumulative timer circuit 43, the volume integrating circuit 44, the large gain decreaser circuit 45 and the second volume integrating detector circuit 41 are backward-acting and are connected to the output conductors I6 and ll of the transmitting channel The syllable counting circuit 46 is connected to a hybrid coil 48. The hybrid coil 48 is connected between the input conductors 9a and I and the output conductors I6 and H of the transmitting channel I. A suitable amplifier 49 is connected between the input conductors 9a. and I9 and the hybrid coil and a second suitable amplifier 59 is connected between the output conductors l6 and I1 and the hybrid coil 48. If the syllable counter-circuit 46 were connected only to the input conductors 9a and ID, the sensitivity of the circuit wouldbe limited by noise operation to such a value that on low input volumes the counter would only be operated on very strong syllables. The rate of counting of weak input speech impulses would then be liable to be less than on strong speech. In order to reduce this difliculty, the syllable counter-circuit 46 is connected through the hybrid coil 48 to both the input conductors 9a.and l9 and the output conductors l6 and 1. This enables speech currents toreach the syllable counter-circuit by two paths, one directly con-' nected to the hybrid coil and the other through the variorepeater and line amplifiers. The sensitivity of the latter path is adjusted so that it is equal to the first path when the gain control circuits are about 30 decibels. v

The volume integrating detector circuit 44v effectively counts the number of volume indicator deflections during a given period of time. The cumulative timer circuit 43 determines the time interval during which the deflections are counted. The cumulative timer circuit 43 comprises an amplifier connected tothe output conductors l6 and ll of the transmitting channel I. The output from the amplifier 5| is connected by a transformer 52 to a detector tube 53. The output circuit for the detector tube is connected to the coil of a relay 54. Plate potential for .the de-' tector tube 53 is supplied by a battery 55 in series with the coil of the relay 54. A battery 56 supplies grid biasing potential and a battery 51 supplies filament heating current for the detector tube 53. Two by-pass condensers 58 are associated with the detector tube 53. An armature 59 of the relay 54 completes a circuit from a battery 60 for operating a relay 6| upon energization of the relay 54. Two resistance elements 62 and 63 and a condenser 64 are provided for effecting a hangover in the operation of the relay 6|.

The relay 6| is preferably given a hangover of .015 second, so that it will hold over between the vocal peaks of speech. The relay 6| is provided with an armature 65 which completes a circuit from a battery 66 to charge a condenser 61 when the relay is operated. The circuit completed by the armature 65 extends from grounded battery 66 through a resistance element 68, armature 65, resistance element 69, condenser 61, a grid biasing battery 19 and ground return to the battery 66. The condenser 61 is connected in the grid circuit of a detector tube 1| which controls a relay 12. A battery 13 supplies anode potential tothe detector tube 1| in series with the coil of the relay 12. The biasing battery is connected to the grid of the tube 1| in circuit with the condenser 61.

Normally, sufficient plate current does not flow through the detector tube 1| to operate the relay 12 and no operation of the relay 12 can take place until a sufiicient charge has been built on the condenser 61. The relay 12 is provided with an armature 14 which completes a circuit from a battery for operating relays 16 and 11. The relay 16 is provided with two coils 18 and 19 and an armature 89 and is included in the integrating detector circuit 44. The relay 11 is provided with an armature 8| which operates between contact members 82 and 83. The relay 11, when released and the armature 8| is in engagement with the contact member 83, completes a circuit from battery 84 through coils 81 and 98 of polarized relays 85 and 86. The relay 85 is provided with the holding coil 81, a releasing coil 88 and an armature 89. The relay 86 is provided with the holding coil 99, a re leasing coil 9| and an armature 92. The coil 99 of the relay 85 operates as a holding coil and the coil 9| opposes the action of coil 99. The coil 9| when energized releases the armature 92 to discharge the condenser 61 in circuit with a resistance element 93. The coil 81 of the relay 85 serves as a holding coil and the coil 88 opposes the action of the coil 81. The coil 88 when energized releases the armature 89 to discharge a condenser 94 through a circuit including a resistance element 95. Either coil 18 or 19 of the relay 16 serves to operate the armature 89 to discharge a condenser 96 in circuit with a resistance element 91.

When the relay 11 is energized and the armature 8| is moved from engagement with the con tact member 83 and into engagement with contact member 82, the holding circuit from the battery 84 through the coils 81 and 96 of the relays 85 and 86 is broken. However, the relays 85 and 86 are held operated a predetermined time by a hangover circuit comprising condenser 98 and a resistance element 99. After the hangover time, relays 85 and 86 release and discharge condensers 94 and 61 through resistances 95 and 93, respectively. The armature 8| of the relay 11 when in engagement with the contact member 82 completes an operating circuit from the battery IOI for operating relay I00. The operating circuit for the relay I00 extends from ground through the armature 8|, contact member 82, resistance elements I02 and I03, coil of relay I00, battery WI and ground return to the armature III. A condenser I 04 provides a hangover in the operation of the relay I00 when the relay TI is released. The relay I00 is provided with an armature I05 which operates between contact members I 06 and I01. The'armature I05 when in engagement with the contact member I07 completes a circuit from the battery I0! under certain conditions for energizing the gain lowering magnet 29. The armature I05 when moved into engagement with the contact member I86 completes a circuit from the battery I0! under cer tain conditions for energizing the gain raising magnet 30.

The first volume integrating detector circuit 44 comprises an amplifier I03 which is connected to the output conductors I6 and I! of the transmitting channel I. The amplifier I08 is connected by a transformer I09 to a rectifying amplifying tube IIII. The tube IIO comprises a cathode III, grid H2, two rectifying anodes IIS and II4 and an amplifying anode H5. The tube rectifying anodes H3 and H4 are connected to opposite terminals of the divided secondary winding for the transformer I99 and serve as a full wave rectifier. The rectifying circuit includthe anode II3 may be traced from the anode II3 through the top portion of the secondary winding of the transformer I89, resistance element H6 and resistance element III to the cathode III. A like circuit may be traced from the anode H4 to include the lower portion of the secondary winding of the transformer I09. The resistance element III which is shunted by a condenser H8 is connected between the grid and cathode of the triode portion of the rectifier-amplifier tube H0. The circuit consisting of the tube I I0 and the condenser-resistance network including resistances H6 and, I I! and condensers H8 and 30! is designed to simulate the action of a volume indicator for a fairly wire range. Battery I I9 is provided for supplying potential tothe anode II5 of the tube H0. A battery I is provided to increase the available plate potential over that obtained from battery IIS, thereby increasing the range somewhat.

Two marginal relays I2I and I22 are provided in the output circuit of the amplifier portion of the tube IIO. The relays I2I and I22 are normally operated. The relay I22 is released when the integrated amplitudes of the syllables of the transmitting channel are above a predetermined level. The relay I2I is released when the integrated amplitudes of the syllables of the transmitting channel are above a second predetermined level. Preferably the second marginal relay I2I is two decibels less sensitive than the relay I22. Normally, the plate current flowing through the amplifier portion of the tube III) operates both relays I2! and I22. Negative grid bias for releasing the relays I2! and I22 is prov1ded by the voltage drop across the resistance element II'I. Condensers H8 and I in combination with the resistances II! and H6 serve to integrate the signals over a period of time.

The relay I22 is provided with an armature I23 which operates between contact members I24 and I25. The relay I2I is provided with an armature I26 which operates between contact members I21 and I28. The relay I22 when in operative position completes a circuit for charging a condenser I29 from battery I30. The circuit for charging the condenser I29 may be traced from the grounded battery I30, through armature I3I of relay I32, contact member I33, contact member I24, armature I23, resistance element I34, condenser I29, battery I and ground return to the battery I30. When the relay I22 is released and the armature I23 is moved into engagement with the contact member I25, the charge on the condenser I29 is impressed on a condenser 96. The condenser l29 is relatively small as compared with condenser 96.

The relay I 2I when in operative position and when the armature I26 is in engagement with the contact member I2! completes a circuit from the battery I36 for charging a condenser I31. The circuit for charging the condenser I3I may be traced from grounded battery I36 through contact member I21, armature I26, resistance element I38, condenser I31, battery I39 and ground return to the battery I36.

Two three-element space discharge tubes I 40 and I M are controlled according to the charge on the condenser 96. The condenser 96 impresses positive potential on the grids of the tubes I40 and MI in opposition to the biasing battery I35. A, relay I42 is included in the output circuit of the tube I M and a relay I43 is included in the output circuit of the tube I40. Plate potential for the tube MI is supplied by a battery I44. Plate potential for the tube I40 is supplied by the battery IOI. The plate current of tube I4I increases as the charge on the condenser 96 increases and when the marginal relay I22 has been released twice the relay I42 is operated. The tube I40 is operated in a manner to be hereinafter described when the relay I22 has been released five times or when the relay I2I has been released four times, The relay I 42 is provided with an armature I45 which is adapted to engage a contact member I46. Upon operation of the relay I 42, a circuit is completed from a battery I41 for operating a relay I48. Resistance elements I49 in combination, with the condenser I50 establish a hangover circuit for the relay I48. The relay I48 is provided with an armature I5I, which is adapted to engage a contact member I52 in the released position. The armature I5I of the relay I48 is included in the operating circuit of the gain raising magnet 30 and no increase in the gain can take place in response to action of the cumulative timer ciricfuit 43 unless the relay I 48 is in released posi- The space discharge device I40 is gas-filled and triggers off when a predetermined potential is impressed on the grid. The output circuit of the device I40 is shunted by condenser I53 and a resistance I54 for providing an oscillatory circuit which assists in extinguishing the arc. The relay I43 which is controlled by the device I40 is provided with an armature I55 which operates between contact members I56 and I57. Upon operation of the device I40, either decibel or 3 decibels reduction in gain is effected.

The charge on the condenser 94 controls the grid of a space discharge device I58. A relay I59 having an armature I60 which engages a contact I6I and a relay I62 having an armature I63 Which engages a contact member I64 are controlled by the device I58. Anode potential for the device I58 is supplied from a battery I65 in series with the coils of the relays I62 and I59. Upon operation of the relay I62 and an engageturn to the battery 84.

merit between the armature I63 and contact I64 condensers I66 and I6I are connected inparallel fora purpose to be later explained. The relay I 59 when operated grounds the grid of the device I40 through a resistance element I68.

The cumulative timer circuit 43 initiates a gain increase of decibel whenever the gain is so low in the time interval that there have not been two operations of the relay I22 in the volume integrating detector circuit 44. The cumulative timer circuit, the same as the large gain decreaser circuit 45, is peak-operated. Syllable's of speech on the transmitting channefl are amplified by the amplifier and supplied to the detector tube 53. The relay 54 is operated according to the detected signals. The relay 6| is operated by relay 54 on each syllable of speech that reaches above the marginal operating value of the relay. The relay M has a .015 second hangover, which causes it to remain operated throughout the syllable as long as the peaks exceed the marginal opera-ting requirement. During the time the relay BI is held'operated, the condenser 67 is charged from the battery 66 through the high resistance 69 and resistance 68. The condenser 67 is in the grid! circuit of the space discharge device II and therefore controls the space current of the device II.

At the start of each time interval which is measured by the cumulativetimer circuit 43, the charge on the condenser E! is zero and the tube or device His biased by the battery I0 so that no plate current flows. Upon operation of the relay 6| and charging of the condenser 6! the grid of the device II becomes more positive and. current flows in the plate circuit through the coil of the relay I2. Upon a predetermined plate current fiow through the tube II the relay I2 is operated. The time interval to effect operation of the relay I2 is generally taken as five seconds. In connected conversational speech this usually requires a lapse of time of about seven seconds. Upon operation of the relay I2 a circuit is completed by the armature I4 for energizing coils of the relays I6 and I! from the battery I5. Operation of the relay I6 completes a circuit for discharging the condenser 96 through the resistance element 91. V Y v Operation of the relay 1! breaks the holding circuit through the coil 90 of the relay 86 and the coil 81 of the relay 85. This holding circuit extends from grounded battery 84 through coil 81, coil 96, resistance 99, resistance I69, contact member 83, armature 8I and ground re- The relays 86 and 85 are held operated for a predetermined length of time by reason of the hangover produced by the condenser 98. When the armature 8| of the relay II engages the contact member 82, a circuit is completed from the battery IIII for operating the relay I00. Upon operation of the relay I00 a circuit is completed from the battery IOI for energizing the gain increase magnet, 30. The circuit for energizing the gain increase magnet 30 may be traced from grounded battery IOI through armature I05, contact member I06, contact member I52, armature I5I of the relay I48, slip ring 34, magnet 30, slip ring 34, and ground return to the battery IOI,

The amount of gain increase is proportional to the length of time the clutch magnet 30 is held energized. The time the clutch magnet is held energized is determined by the hangover of the relay 86 and the hangover of the relay I00. The hangover time of these relays has been adjusted so that the total increase in gain is about decibel. The-hangover of the relays 86 and 85 becomes efiective when the relay I'I operates and removes ground from the resistance element I69. The operation of the relay II permits the condenser 98 'to charge and when the charging current becomes small the relays 66 and 85 are released. The release of the relay 86 discharges the condenser 61. The release of the relay 85 discharges the condenser 94. When the condenser 67 is discharged, the grid of the tube II is again made negative, the plate current is reducecl to zero and the relays I2, I1 and I6 are released. The release of the relay I6 removes the shunt across the condenser 96. The release of the relay II removes the ground from the operating circuit of relay I60 and applies it to the holding circuit of relays B6 and 85. The relays 85 and 85 when operated remove the shunts across the condensers 61 and 94 and a new timed interval is started.

If in a time interval as measured by the cumulative timer circuit 43, two, three or four operations of the relay I22 have taken place, then the relays I42 and I48 are operated, as will be explained. Operation of the relay I48 opens the circuit of the gain increase magnet 30 and therefore no gain increase can be effected by operation of the cumulative timer circuit 43 as above described.

The marginal relays I2I and I22 in the volume integrating circuit I44 are operated according to the strength of the syllables on the transmis-- sion channel I. The amplified signals supplied from the transmitting channel are rectified by the diode portion of the tube IIO, integrated by condensers II8 and 30I and the resistances II! and H6, and amplified by the triode portion of the tube IIO for operating the relays HH and I22 according to the strength of the syllables. If in any given time interval five syllables are strong enough to operate the relay I22 or four syllables are strong enough to operate the relay I2I which is 2 decibels less sensitive than the relay I22, a gain decrease is made and a new integrating interval is started. Upon each release of the relay I22 the condenser 96 is charged by the charge of the condenser I29. .The condenser I29 is charged from the battery I30 when the relay I22 is in operative position. The condenser 96 is in the grid circuit of the tubes I40 and I M.

When the relay I22 is released twice and. two charges are transferred from the condenser I29 to the condenser 96, then the grid bias on the tube MI is reduced so that the plate current of the battery I44 operates the relay I42. The armature I45 of the relay I42 completes a circuit from battery M7 for operating the relay I48. The armature I5I of the relay I48 breaks the operating circuit of the gain increase clutch magnet 30. so that no increase in gain can take place under control of the cumulative timer circuit 43 when the relay I48 is operated. No further circuit changeoccurs until the fifth release of the relay I22. .The fifth charge transferred from the condenser I29 to the condenser 96 causes ionization of the'gas tube I40. Upon breakdown or triggering off of the tube I40, a circuit is completed for energizing the gain decrease magnet 29. This circuit may be traced from ground battery I 0| through the armature I85 of relay I00, contact member I01, slip ring 3|, magnet 29, second slip ring 3|, resistance I10, armature I55 of the relay :I43, contact member I5I, space discharge device I40 and ground return to the battery I9 I. At the same time current flows from the grounded battery IOI through armature I05, contact member I61, resistance element I1I, coil 9! of the relay 86, coil 88 of the relay 85, coil 18 of the relay 16', coil of relay I43, device I40, and ground return to the battery WI. The building up of current in the windings of the relays 86, 85, 16 and I43 is retarded by the shunting effect of condenser I61. When the condenser I61 has become sufficiently charged relays I43 and 16 operate while the relays and 86 are released.

Operation of the relay I43 interrupts the current flowing through the gain decrease magnet 29. The gain decrease magnet 29 is operated about .002 second in order to effect a gain decrease of about decibel. Operation of the relay 16 discharges the condenser 96, permitting release of the relays I42 and I48 and extinguishing'the ionization of the gas-filled device I40. The relay I43 and the'relay 16 are then released. The releasing of the relays 86 "and 85 discharge the condensers 61 and 94, so thata new integrating interval can be started.

If the volume on the transmitting channel I is somewhat higher'so that the relay I2I is frequently operated, the gain decrease may become 3 decibels instead of decibel. The relay I'2I when released transfers charge from the condenser I31 to the condenser 94 in the same manner as the relay I22 transfers charge from'the condenser I29 to the condenser 96. The charge on the. condenser 94 controls the potential on the grid of the tube I58. When three charges from the condenser I21 have been impressed on the condenser 94, the plate current of the tube I58 is raised sufficiently to 'effectoperation of the relay I62. Operation of therelay I62 connects the condenser I66'in shunt to the'conde'n'ser I61. Connecting the condenser I66 in shunt to the condenser I61 decreases the rate at which current builds up in the coil 9| of the relay 86, coil 88 of the'rela'y 85, coil 18 of the relay 16 and thecoil of the relay I43 when the device I40 ionizes. The device I40 does not ionize, however, until the relay I22 operates the fifth time orthe relay I2I releases the fourth time within the same time interval asmeasured by the cumulative timer circuit 43. If the relay I22 releases the fifth time within the interval, the action is identical to that described above for the condition of five operations of the relay I22 and no operation of the relay I2I except that the amount of gain decrease is 3 decibels. The change in the amount of gain decrease is effected by the condenser I66 in shunt to the condenser I61. The condenser I66 connected in shunt to the condenser I61 delays the release of the relays 86 and 85 and the operation of the relays 16 and I43.

If before the relay I22 operates the fifth time, the relay I2I operates a fourth time within the time interval, the plate current of the device I58 becomes great enough to operate the relay I59. Operation of the relay I59 connects the grid of the tube I40 to ground through the resistance element I68 and the tube immediately ionizes, causing a S-decibel gain decrease as above set forth and a new interval is started. Grounding of the grid of the tube I40 by the" relay I59 reduces the negative bias on the tube.

The fast or large gain decrease circuit 45 comprises an amplifier I13 connected to the output conductors I6 and I1 of the transmission channel. The amplifier I13 is connected by a transformer I14 to diode triodespace discharge deconnected'to the segment 2I3.

vice I15. The amplifier portion or triode portion of the device I15 is connectedto a relay I16; The anodes I11 and I18 of the device I15 are connected to'terminals of separate secondary windings for the transformer I14. The cathode I19 of the device I15 is connected through a resistance I80 shunted by condenser I8I to a common terminal of the secondary windings of the transformer I14; The anode of the triode portion of the device I15 is supplied with potential from a battery I82 in circuit with the coil of the relay I16. The relay I16 is normally operated and is released only when sufiicient negative potential is impressed on the grid of the triode portion of the device I15.

The fast decreaser circuit '45 produces a gain decrease on any syllable with a peak that extends above the marginal operating level of the fast decreaser circuit. The syllables build up 'a charge on the condenser NH and this biases the grid'of 'the'triode portion of the device I15 negatively to reduce the plate current; When the plate current falls sufficiently the relay I16 is released; Release of the relay I16 completes a circuit for energizing the gain decrease magnet 29. The circu-it completed by the release of the relay I16 may be traced from ground through armature I83, contact member I84, resistance I85, resistance I10, oneslip ring 3|, magnet 29, the other slipring 3|, contact member I01, armature I05 and grounded battery IOI. The amount of gain decrease is determined by'the length of time the relay I16 is released. This isdetermined by the length of time the syllable peaks remain above the marginal operating value. When the gain has been decreased so that the peaks are no longer high enough to hold the relay I16 released, the relay pulls up and'prevents further gain decrease.

The syllable counter circuit 46 comprises an amplifier I86 which is connected to the hybrid coil 48 'by transformer I81. The hybrid coil 48 as abovesetforth is connected between the input conductors 9a and I0 and the output con ductors I6 and I1 of the transmitting channel I but is isolated by amplifiers 49 and 50. The output'circuit of the amplifier I86 is connected by transformer I88 to two detector tubes I89 and I90. The detector tubes I89 and I90 are connected by a transformer I9! to a filter I92 which "selects syllable frequencies. The filter I92 is connected to a coil I93 of a relay I94. The relay I94 which is a polarized relay isprovided with a second coil I95 which is energized from a battery I96. The relay I94 is provided with an armature I91 for completing a circuit from battery I98 to energize a coil I99 of'a relay 200. The relay 200 is provided with a second coil 20I which is energized from the battery I96 and an armature 202 which engages the contact member 203 upon operation of the relay 200 for completing a circuit through a. stepping magnet 204 of a counting device 205. The circuit to the stepping magnet 204 may be traced from a grounded battery 205a, armature 206 of relay 201, contact member 208, resistance 209, stepping magnet 204, armature" 202 of relay 200, contact member 203 andground return to the battery 205a.

The counting device 205 comprises two switch arms 2I0 and 2 which are given a rotative movement under control of the stepping magnet 204. The arm 2II bridges contact elements 2I2 and a contact segment 2I3. A battery 2I4 is The arm 2I0 engages a switch member 2I5 in the initial position of the counter 205 to connect a battery 2l6 to a contact member 2I1. Upon starting of the counting device the member 2I5 connects the battery 2I 6 to a contact member 2I8. A release output conductors I6 and I1 of the transmitting The amplifier 220 is connected by a channel I. transformer 22I to an integrating detecting circuit including a diode triode space discharge device 222. The diode portion of the device 222 comprises two anodes 223 and 224, which are connected to opposite terminals of the divided secondary swinding of the transformer-22L The triode portion of the device 222 comp-rises an anode 225, a grid 226 and a cathode, 221. One rectifying circuit for the diode may be traced from the anode 224 through the upper portion of the secondary ;;winding for the transformer 22!, resistance ele- Three marginal polarized relays 234, 235 and 236 are controlled by the diode triode device 222.

The relay 234 comprises an operating. winding 231, a biasing winding 238 and an armature 233 which operates between contact members 240 and 24!. The relay 235 comprises an operating winding 242, a biasing winding 243 and an armature 244 which operates between contact members ,245 and 246. The relay 236 comprises an operating winding 241, a biasing winding 248 and an armature 249, which operates between contact members 250 and 25I. The relay 234 controls the hangover of relay 201 as determined by discharging of a condenser 252 in circuit'with a resistance element 253. The relay 235 controls the hangover vof relay 201 as determined by discharging Of condenser 254 in circuit with a resistance element 255. The relay 236 controls the hangover of relay 201 as determined by discharging of a condenser 256 in circuit with the relay 251.

In case of low volume on the transmitting channel I, the gain changes effected by the cumulative timer circuit 43 and the volume integrating detector circuit 44 maybe too small and infrequent to raise the volume in the required time. The syllable counter 46 and the volume integrating detector circuit 41 operate to produce much larger gain increases. The input voltage of audio frequency is amplified by the amplifier I86 and is detected by the tubes I89 and I96. The variations of syllable frequencies areselected by the filter I92. The relay I34 is ope-rated by the impulses of syllable frequency for completing a circuit from the battery I98 to effect operation of the relay 200. The circuit for operating the relay 200 may be traced from the battery I98 through the coil I99 of the relay 200, resistance elements 265 and 266, armature I91 and ground return to the battery I23. The condenser 264 which is connected between ground and the two resistance elements 265 and 266 serves to effect a hangover in the operation of the relay 250. The relay 256 .upon operation bya strong syllable completes a circuit for energizingnthe stepping magnet 204. The circuit for operating the step-ping magnet 204 may be traced from grounded battery 2056: through the armature 206 of the relay 201, contact member 208, resistance 266, stepping magnet 204, armature 202 of the relay 200, contact mem her 203 and ground return to battery 205a. The relay 201 at this time is held in operative position by a circuit which extends from grounded battery 205a through armature 206 of relay 201, contact member 208, armature 21I of relay 210, contact member 213, resistance elements 268 and coil of relay 201 and ground return to battery a.

Upon operation of the stepping magnet 204, the arms 2H and 2I0 of the counter mechanism 205 are operated one step. On each succeeding operation of the relay 200, the counter steps another step. When the counter reaches the sixth position the operating circuit of the relay 210 is energized. The energizing circuit for the coil of the relay 210 extends from grounded battery 2I4, through switch segment 2| 3, arm 2, sixth contact member on the counter, resistance elements 214 and 215, coil of relay 210 and ground return to battery 2l4. The relay 210 operates with suflicient hangover by reason of a condenser 216 to hold over during latter stepping movements of the counter so that it remains in operative position until the counter is released and returned to zero. Operation of the relay 210 removes the battery 205a from the holding circuit of the relay 201.

The relay 201 has a hangover the amount of which is determined by the position of the relays 234, 235 and 236. The relays 234, 235 and 236 are normally held in operative position by the plate current flow through the triode of the de vice 222. When the above-mentioned relays are in operative position the armatures 239, 244 and 249 apply ground to the condensers 252, 254 and 256. The condensers 252, 254 and 256 are also connected to the battery 205a by a circuit which ext-ends from the grounded battery 265a. through armature 206 of relay 201, contact member 208, armature 21I of relay 216 and resistance element 269 to the condensers 252, 254 and 256. The total hangover time of the relay 201 depends on the number of condensers 252, 254 and 256 which are charged and connected to ground when the energizing circuit of relay 216 is broken. The release of any of the relays 234, 235 and 236 removes the ground from the condenser 252, 254 and 256 and therefore changes the hangover time of the relay 201. When the output volume on the transmitting channel is very low all three relays 234, 235 and 236 will remain operated and relay 201 will have a maximum hangover time.

Operation of the relay 210 energizes the in.- crease gain clutch magnet 36 by a circuit which extends from grounded battery 205a through the armature 206 of relay 201, contact member 258, armature 21I of relay 210, contact member 212, one of the slip rings 34, gain increase magnet 30, the other slip ring 34 and ground return to the battery 20511. When all three hangover condense-rs 252, 254 and 256 are effective the relay 201 remains operated for a time which will permit the gain to increase a large amount, for ex-- ample 15 decibels.

If only the condensers 252 and 254 are effective the relay 201 will remain operated a sufficient time to efiect 8 decibels gain. If only the relay 252 is effective the relay 201 will remain perative a suificient time to effect 3 decibels 2:-

gain. 2% is efiective, no gain will take place.

Upon release of the relay 207 the circuit from.

the battery 205a through the gain increase mag- 5 net 38 is broken. When the armature 206 of the relay engages the contact member. 21? the release magnet 2!!! is energized by a circuit which extends from the grounded battery 205a through armature 2% of relay 2371, contact memmlber 2H, resistance element 218,. coil of release magnet Eli); and ground return to the battery 285a. The release magnet 2I9 causes the arms 2m and 2i i to return to zero, position. The arm 25 I upon return to zero position removes battery 5 ,from the operating circuit of the relay 219. When the counter arm 2E0 reaches zero position the switch member Zillis separated from the contact member M8 and is moved into engagement with contact member 275?. The separating of o the switch arm 2I5 from contact member 2i8 'disconnects the battery 2 I 6 ,from any of the bias ing coils 238, 2 13 and 2&8 oi the relays 234, 235 and 236. The engagement between the switch arm Hi5 and the contact member 2I'i serves gssto energize the relay 291 from the battery 2I6.

At this time operation of relay 2M applies potential from the battery 2535a through the resistance element E269 and the coil of the relay 207. The relay 2M will again be held in operative ag position by current supplied by the battery 235a.

" When the output volume on the transmitting channel is not very low one or more of the speech syllables will build up a sufficient charge on, the condenser 23B of the Volume integrating deteclfi tor circuit 4? to reduce the plate current through "the triode of the device 222 suiiicient to release one or more of the relays 23 i, 235 and 236. l/Vhenever one of the relays 234, 235 and 236 is released, ground is applied to the biasing wind- 4Q :;ing associated therewith. The circuit of the biasing Winding 2:23 for the relay'236 may be traced from grounded battery ZIG through-contact arm 2I5, contact member 2I8, coil 268, contact member 250, armature 249 and ground re- 1;;turn to the battery 2I6. When one of the relays 234, 235 and 236 has been released and held by its biasing winding the relay cannot pull out and be operated until the syllable counter circuit is returned to zero position.

42;; When the volume control circuits are used as a part of a four-wire circuit the echoes of the received speech may operate in the various control circuits unless provision is taken. to prevent such operation. An amplifier detector'258 is connected to the receiving channel 2 for operating relays 259 and I32 whenever the receiving channel is in service. The relay 259 when oper-- ated completes a circuit from the battery 205a through the armature 262 and resistance 218 for "operating release magnet MB. This insures that the syllable counter would be in zero position and that the relays 234, 235 and 235 will be in normal position. The relay I32 is provided with an armature 23: which short-circuits the gain decrease magnet 29 to prevent any operation thereof when speech is on the receiving channel. Armature I3I of the relay I32 disconnects the battery E36 from the condenser I29 and prevents 7 any charging thereof. The condenser I29 charges J the condenser 9% which in turn controls the gain decrease by means of the space discharge devices Mil and MI. The armature 266 operated by the relay I32 impresses negative potential on the grid H2 in the triode of the space discharge de- If none of the condensers. 252 254.and:

vice IIIi so :as to prevent operation-of either marginalrelay I21 and I22.

Modifications inthe circuits and in the arrangement. and location ofparts may bemade within the spirit and scope of the invention and such modifications are intended to be covered by the appended'claims.

What is claimed is:

1. The method of controlling the volume of signals on .atransmission line which consists in detecting and counting the. number of amplitude variations above a predetermined value on the transmission line, inv determining time intervals during which amplitude variations are counted, and in varying the gain on the transmission line according to thenumber and value of the amplitude variations above a predetermined value detected during a time interval.

2. The method'oi controlling the volume of signals on a transmission line which consists in detecting and counting. the number of amplitude variations above a predetermined value on the transmission line, in determining according to the speed of amplitude variations on the line the time intervals during which amplitude variations are counted, in raising the gain on the transmission line whenless than a minimum number of volume variations above a predetermined value are detected in one time interval, and in preventing raising of the gain on the line when a predetermined minimum number of Volume variations above a predetermined value are detected in one time interval.

3. The method of controlling the volume of signals on a transmission line which consists in detecting and counting the number of amplitude variations above a predetermined value on the transmission line, in determining according to the speed of amplitude variations on the line the time intervals during which amplitude variations are counted, in raising the gain on the transmission line when less than a minimum number of amplitude variations above a predetermined value are detected in one time interval, and in lowering the gain on the transmission line when a predetermined number of variations more than a minimum number of volume variations above a predetermined value are detected in one time interval.

4. A signal transmission line having a gain varying device therein, a volume indicating detector circuit for counting the number of amplitude variations above a predetermined value on the transmission line, a timer circuit operated according to the speed of the amplitude variations on the line for determining the time interval during which the amplitude variations are counted, and means governed by said timer circuit at the end of a time interval for operating said gain device to increase the gain a small amount when the volume indicating detector circuit has not received a predetermined minimum number of amplitude variations above the predetermined value.

5. A signal transmission line having a gain varying device therein, a volumeindicating detector circuit for counting the number of amplitude variations above a predetermined value on the transmission line, a timer circuit controlled according to the speed of the amplitude variations on the line for determining the time interval during which the amplitude variations are counted, means controlled by said volume indicating circuit when only a predetermined minimum number of amplitude variations :above the predetermined value occur-for preventing operation of said device, and means governed by said timer circuit at the end of a time interval when less than the minimum number of amplitude variations above the predetermined value occur for operating said device to increase the gain on the line a small amount.

6. A signal transmission line having a gain varying device therein, a volume indicating detector circuit for counting the number of amplitude variations above a predetermined value on the transmission line, a timer circuit governed according to the speed of the amplitude variations on the line for determining the time interval during which the amplitude variations are counted, means governed by said timer circuit for operating said gain device to increase the gain on the line a small amount if the amplitudes on the line in a time interval are a small amount below normal, and means controlled by said volume indicating detector circuit for operating said gain device to lower the gain on the line a small amount when the amplitudes on the line in a time interval are a small amount above normal.

7. A signal transmission line having a gain varying device therein, a volume indicating detector circuit for counting the number of amplitude variations above a predetermined value on the transmission line, a timer circuit for determining the time interval during which the amplitude variations are counted, marginal means controlled by said volume indicating circuit, means controlled by said marginal means for effecting diiferent amounts of gain reduction by said device according to the value of the amplitude variations counted, and means controlled by said timer circuit for operating said device to effect a small increase in gain upon failure of a predetermined minimum operation of said marginal means.

8. A signal transmission line having a gain varying device therein, timing means for measuring the time the signals on the transmission line are above a certain level to determine a time interval, indicating means for detecting the number of amplitude variations above a predetermined value in a time interval, means governed by said timing means for operating said device to increase the gain on the line when a predetermined minimum number of amplitude variations are not detected by said indicating means in a time interval, and means governed by said indicating means for preventing operation of said device by said timing means when a minimum number of amplitude variations above a predetermined value are detected, and for operating said device to lower the gain on the line according to the number and the value of the detected amplitude variations above the predetermined value when more than a minimum number of variations are detected.

9. A signal transmission line having a gain varying device therein, a volume indicating de tector circuit for counting the number of amplitude variations above a predetermined Value on the transmission line, a timer circuit for determining the time interval during which amplitude variations are counted, marginal relays selectively operated by said indicating circuit, means governed by said timing circuit at the end of a time interval when less than a predetermined minimum number of amplitude variations have been detected by said indicating circuit for operating said device to increase the gain on the line, means operated by one of said relays for preventingoperation of said device by the timing circuit when "a minimum number of amplitude variations are detected by said indicating circuit and for. operating said device to lower the gain on the line a small amount when a predetermined number of amplitude variations above the minimum number of amplitude variations are detected by said indicating circuit, and means operated by another one of said relays for operating said device to effect a greater loss in the gain on said line when a number of amplitude variations of greater value are detected by said indicating circuit.

10. A signal transmission line having a gain varying device therein, a volume indicating detector circuit for integrating and counting the variations above a predetermined value for operating said device to effect small decreases and increases in gain on the line, and fast decreaser means for operating said device at a fast rate to lower the gain on the line when syllable peaks go above a predetermined upper level.

11. A signal transmission line having a gain varying device therein, a volume indicating detector circuit for integrating and counting the number of amplitude variations above a predetermined value on the transmission line, a timer circuit for determining the time interval during which the amplitude variations are counted, means governed by said timer circuit at the end of a time interval for operating said device to increase the gain a small amount when the volume indicating detector circuit has not received a predetermined minimum number of amplitude variations above the predetermined value, means operated by said indicating circuit for operating said device to lower the gain on the line by varying amounts according to the value and number of amplitude variations detected above the predetermined minimum number, and fast decreaser means for operating said device at a fast rate todecrease the gain on the line when syllable peaks go above a predetermined upper level.

12. A signal transmission line having a gain varying device therein, means comprising a syllable counter operated by syllables on the line, gain increaser means operated by said counter when a predetermined number of syllables have been counted for operating said device to increase the gain on said line by a substantial amount, and marginal means operated according to the energy values of the syllables on the line to vary the amount of increase in gain effected by said gain increaser means.

13. A signal transmission line having a gain Varying device therein, means comprising a syllable counter operated by syllables on the line, gain increaser means operated by said syllable counter when a predetermined number of syllables have been counted and the syllables are below a predetermined energy level for operating said device to increase the gain on the line by a substantial amount, and means for selectively varying the increase in gain caused by said gain increaser means according to the energy Value of the syllables and for preventing operation of the gain increaser means when the syllables are above a predetermined energy value.

14. A signal transmission line having a gain varying device therein, means comprising a syllable counter operated according to the number of syllables on the line, gain increaser means operated by said syllable counter when a predetermined number of syllables have been counted and the syllables are below a predetermined energy level for operating said device to increase the gain on the line by a substantial amount, means for selectively varying the increase in gain caused by said gain increaser means according to the energy value of the syllables and for preventing change in gain by the gain increaser means when the syllables are above a predetermined energy level and auxiliary means for controlling said device according to amplitude of the signals to efiect small changes in gain on the line.

15. A signal transmission line having a gain varying device therein, a Volume indicating detector circuit for integrating and counting the number of amplitude variations above a predetermined value on the transmission line, a time circuit for determining the time interval during which the amplitude variations are counted, means comprising a syllable counter operated according to the number of syllables on the line, gain increaser means operated by said syllable counter when a predetermined number of syllables have been counted for operating said device to increase the gain on the line by a substantial amount, marginal means operated according to the energy values of the syllables on the line for Varying the amount of increase in gain by said increaser means and for preventing change in gain by the increaser means when the syllables are above a predetermined value, and means governed by said time circuit and said indicating circuit according to the amplitude variations above a predetermined value for operating said device to effect small decreases and increases in gain on the line.

16. A signal transmission line having a gain varying device therein, a volume indicating detector circuit for counting the number of amplitude variations on the transmission line above a predetermined value, and means governed by said detector circuit for controlling said device to lower the gain on the transmission line according to the number and strength of the amplitude variations above the predetermined value.

BJORN G. BJORNSON'. NEWTON W. BRYANT. 

